Laser welding can have high-energy density and can achieve a large depth of penetration and high speed welding. Thus, laser welding is expected as a high-efficiency welding method. Since the laser welding causes melting at extremely localized points, the effect of heat applied to a workpiece (for example, a thin steel sheet, a thick steel plate, a stainless steel plate, or a stainless steel sheet) is small and distortion or deformation is slight, leading to a high-quality weld joint. Thus, the laser welding has practically been used in the field of thin steel sheets such as automobile thin steel sheets on an assembly line of members of framework or automobile bodies. Also in the field of thick steel plates, practical use of laser welding has seriously been considered since the weldable plate (sheet) thickness is increased as a result of current commercial sales of highly efficient laser welding machines that can perform optical fiber transmission at high power.
In the laser welding, however, a workpiece rapidly melts because a high-energy density laser beam is converged by an optical component and emitted to a weld portion. Thus, the molten metal may scatter around as spatter from the formed molten weld pool. If the scattered spatter adheres to the workpiece, the external appearance of the weld portion is spoiled. Furthermore, if spatter adheres to a guard glass or an optical component such as a lens, properties of a laser beam such as a focusing property or irradiance level are changed and the performance of the laser welding becomes unstable.
If a large amount of spatter is generated, the amount of molten metal in the molten weld pool decreases, thereby making welding defects such as undercut or underfill (i.e., depression) more likely to occur. The occurrence of undercut or underfill brings about reduction in strength of the weld portion.
In view of these problems, Patent Literature 1, for example, discloses a technology of preventing spatter from scattering into a laser working head by using a laser working head having a double-pipe nozzle configuration and forming a shielding curtain from assist gases ejected from an external nozzle of the head.
Patent Literature 2 discloses a technology of preventing underfill and spatter from occurring by feeding a filler wire to a weld portion subjected to laser welding while swinging the filler wire.
Patent Literature 3 discloses a technology of preventing spatter from adhering to a laser working head and a workpiece by ejecting a fluid sideways to a space between a laser working head and a workpiece.
Patent Literature 4 discloses a technology of preventing spatter from adhering to an optical component or a workpiece by blowing a gas sideways from a position near the workpiece toward spatter scattering from a molten weld pool formed by being irradiated with a laser beam.